définition - aerobic exercise

aerobic exercise(n.)

1.exercise that increases the need for oxygen

Aerobic Exercise(n.)

1.(MeSH)Physical activity which is usually regular and done with the intention of improving or maintaining PHYSICAL FITNESS or HEALTH. Contrast with EXERTION which is concerned largely with the physiologic and metabolic response to energy expenditure.

Aerobic exercise (also known as cardio) is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process.[1] Aerobic literally means "living in air",[2] and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism.[3] Generally, light-to-moderate intensity activities that are sufficiently supported by aerobic metabolism can be performed for extended periods of time.[1]

Aerobic exercise and fitness can be contrasted with anaerobic exercise, of which strength training and short-distance running are the most salient examples. The two types of exercise differ by the duration and intensity of muscular contractions involved, as well as by how energy is generated within the muscle.

In most conditions, anaerobic exercise occurs simultaneously with aerobic exercises because the less efficient anaerobic metabolism must supplement the aerobic system due to energy demands that exceed the aerobic system's capacity. What is generally called aerobic exercise might be better termed "solely aerobic", because it is designed to be low-intensity enough not to generate lactate via pyruvatefermentation, so that all carbohydrate is aerobically turned into energy.

Initially during increased exertion, muscle glycogen is broken down to produce glucose, which undergoes glycolysis producing pyruvate which then reacts with oxygen (Krebs cycle) to produce carbon dioxide and water and releasing energy. If there is a shortage of oxygen (anaerobic exercise, explosive movements), carbohydrate is consumed more rapidly because the pyruvate ferments into lactate. If the intensity of the exercise exceeds the rate with which the cardiovascular system can supply muscles with oxygen, it results in buildup of lactate and quickly makes it impossible to continue the exercise. Unpleasant effects of lactate buildup initially include the burning sensation in the muscles, and may eventually include nausea and even vomiting if the exercise is continued without allowing lactate to clear from the bloodstream.

As glycogen levels in the muscle begin to fall, glucose is released into the bloodstream by the liver, and fat metabolism is increased so that it can fuel the aerobic pathways. Aerobic exercise may be fueled by glycogen reserves, fat reserves, or a combination of both, depending on the intensity. Prolonged moderate-level aerobic exercise at 65% VO2 max (the heart rate of 150 bpm for a 30-year-old human) results in the maximum absolute contribution of fat to the total energy expenditure. At this level, fat may contribute 40% to 60% of total, depending on the duration of the exercise. Vigorous exercise above 75% VO2max (160 bpm) primarily burns glycogen. [4][5]

Major muscles in a rested, untrained human typically contain enough energy for about 2 hours of vigorous exercise. Exhaustion of glycogen is a major cause of what marathon runners call "hitting the wall". Training, lower intensity levels, and carbohydrate loading may allow to postpone the onset exhaustion beyond 4 hours.[5]

Aerobic exercise comprises innumerable forms. In general, it is performed at a moderate level of intensity over a relatively long period of time. For example, running a long distance at a moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity, while golf or two person team tennis, with brief bursts of activity punctuated by more frequent breaks, may not be predominantly aerobic. Some sports are thus inherently "aerobic", while other aerobic exercises, such as fartlek training or aerobic dance classes, are designed specifically to improve aerobic capacity and fitness. It is most common for aerobic exercises to involve the leg muscles, primarily or exclusively. There are some exceptions. For example, rowing to distances of 2,000 m or more is an aerobic sport that exercises several major muscle groups, including those of the legs, abdominals, chest, and arms. Common kettlebell exercises combine aerobic and anaerobic aspects.

Among the recognized benefits of doing regular aerobic exercise are:

Strengthening the muscles involved in respiration, to facilitate the flow of air in and out of the lungs

Strengthening and enlarging the heart muscle, to improve its pumping efficiency and reduce the resting heart rate, known as aerobic conditioning

Strengthening muscles throughout the body

Improving circulation efficiency and reducing blood pressure

Increasing the total number of red blood cells in the body, facilitating transport of oxygen

Improved mental health, including reducing stress and lowering the incidence of depression

Reducing the risk for diabetes.

Burns body fat, while building leaner muscle.

As a result, aerobic exercise can reduce the risk of death due to cardiovascular problems. In addition, high-impact aerobic activities (such as jogging or using a skipping rope) can stimulate bone growth, as well as reduce the risk of osteoporosis for both men and women.

In addition to the health benefits of aerobic exercise, there are numerous performance benefits:

Increased storage of energy molecules such as fats and carbohydrates within the muscles, allowing for increased endurance

Increasing speed at which aerobic metabolism is activated within muscles, allowing a greater portion of energy for intense exercise to be generated aerobically

Improving the ability of muscles to use fats during exercise, preserving intramuscular glycogen

Enhancing the speed at which muscles recover from high intensity exercise

Both the health benefits and the performance benefits, or "training effect", require a minimum duration and frequency of exercise. Most authorities suggest at least twenty minutes performed at least three times per week.[6]

Aerobic capacity

Aerobic capacity describes the functional capacity of the cardiorespiratory system, (the heart, lungs and blood vessels). Aerobic capacity is defined as the maximum amount of oxygen the body can use during a specified period, usually during intense exercise.[7] It is a function both of cardiorespiratory performance and the maximum ability to remove and utilize oxygen from circulating blood. To measure maximal aerobic capacity, an exercise physiologist or physician will perform a VO2 max test, in which a subject will undergo progressively more strenuous exercise on a treadmill, from an easy walk through to exhaustion. The individual is typically connected to a respirometer to measure oxygen consumption, and the speed is increased incrementally over a fixed duration of time. The higher the measured cardiorespiratory endurance level, the more oxygen has been transported to and used by exercising muscles, and the higher the level of intensity at which the individual can exercise. More simply stated, the higher the aerobic capacity, the higher the level of aerobic fitness. The Cooper and multi-stage fitness tests can also be used to assess functional aerobic capacity for particular jobs or activities.

The degree to which aerobic capacity can be improved by exercise varies very widely in the human population: while the average response to training is an approximately 17% increase in VO2max, in any population there are "high responders" who may as much as double their capacity, and "low responders" who will see little or no benefit from training.[8] Studies indicate that approximately 10% of otherwise healthy individuals cannot improve their aerobic capacity with exercise at all.[9] The degree of an individual's responsiveness is highly heritable, suggesting that this trait is genetically determined.[8]

Criticisms

When overall fitness is an occupational requirement, as it is for athletes, soldiers, and police and fire personnel, aerobic exercise alone may not provide a well balanced exercise program. In particular, muscular strength, especially upper-body muscular strength, may be neglected. Also, the metabolic pathways involved in anaerobicmetabolism (glycolysis and lactic acid fermentation) that generate energy during high intensity, low duration tasks, such as sprinting, are not exercised at peak aerobic exercise levels. Aerobic exercise remains however a valuable component of a balanced exercise program and is good for cardiovascular health.

Some people suffer repetitive stress injuries with some forms of aerobics, and then must choose less injurious, "low-impact" forms of aerobics, or lengthen the gap between bouts of exercise to allow for greater recovery.

Higher intensity exercise, such as High-intensity interval training (HIIT), increases the resting metabolic rate (RMR) in the 24 hours following high intensity exercise,[10] ultimately burning more calories than lower intensity exercise; low intensity exercise burns more calories during the exercise, due to the increased duration, but fewer afterwards.

Aerobic activity is also used by individuals with anorexia nervosa as a means of suppressing appetite, since aerobic exercise increases sugar and fatty acid transport in the blood by stimulating tissues to release their energy stores.[citation needed] While there is some support for exercising while hungry as a means of tapping into fat stores, most evidence is equivocal.[citation needed] In addition, performance can be impaired by lack of nutrients, which will reduce training effects.[citation needed]

Commercial success

Aerobic exercise has long been a popular approach to achieving weight loss and physical fitness, often taking a commercial form.

In the 1970s Judi Sheppard Missett helped create the market for commercial aerobics with her Jazzercise program

In the 1980s Richard Simmons hosted an aerobic exercise show on television, and also released a series of exercise videos